Re: Primary Key...Is One Required?

Bonnie >Is it necessary to have a primary key for a table? Not really, but if you are implementing referential integrity from another table, then you do. In this case, it is better to create a named unique index since that is easier to manage. >According to Informix Documentation, if a primary key does not exist for a table, a primary >key is composed of all columns taken together. Does this mean that Informix automatically >generates a primary key? Not as far as I know. It may be interesting to know which FM (with a page number if possible) says this. >Also, I recently attended an Informix Class where the instructor said that Informix does >not automatically generate a primary key. I would tend to agree with him. >I'm now wondering whether or not I should create a serial record_num primary key for this >table because if one is automatically generated out of every column (I have a >large number of columns) and because primary keys are automatically >indexed, this will be a very large/inefficient index. Primary keys are automatically indexed, but a PK is not automatically generated out of evey column, AFAIK. It is interesting that you are thinking of using serial surrogate keys instead of "natural" keys. At each of the sites I have been to, it is one or the other, almost a religious issue :-). HTH Sujit Bonnie Annelin <bonnie_annelin@intuit.com> on 06/02/99 04:37:35 PM Please respond to Bonnie Annelin <bonnie_annelin@intuit.com> To: informix-list@iiug.org cc: (bcc: Sujit Pal) Subject: Primary Key...Is One Required? I have a question regarding primary keys for tables. Is it necessary to have a primary key for a table? According to Informix Documentation, if a primary key does not exist for a table, a primary key is composed of all columns taken together. Does this mean that Informix automatically generates a primary key? I do a database dump (dbschema) and do not see a primary key listed for my table. Also, I recently attended an Informix Class where the instructor said that Informix does not automatically generate a primary key. I'm now wondering whether or not I should create a serial record_num primary key for this table because if one is automatically generated out of every column (I have a large number of columns) and because primary keys are automatically indexed, this will be a very large/inefficient index. Thanks, Bonnie Annelin